Generation of an optical local-oscillator signal for a coherent-detection scheme

Abstract

An optical receiver having an optical IQ modulator configured to generate an optical local-oscillator (OLO) signal for optical homodyne detection of an optical input signal applied to the optical receiver. The optical receiver further has (i) a phase detector configured to generate an electrical measure of the phase difference between the OLO signal and a carrier wave of the optical input signal and (ii) a phase-lock loop configured to drive the optical IQ modulator using the electrical measure. In an embodiment, the phase detector is configured to generate the electrical measure using both I and Q components of the homodyne-detected signal and in a manner that enables the optical receiver to be compatible with the M-QAM modulation format.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]The subject matter of this application is related to that of U.S. Patent Application Publication No. 2014 / 0199068, which is incorporated herein by reference in its entirety.BACKGROUND[0002]1. Field[0003]The present disclosure relates to optical communication equipment and, more specifically but not exclusively, to coherent detection of modulated optical signals.[0004]2. Description of the Related Art[0005]This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.[0006]Coherent detection is used in optical transport systems, for example, because it is compatible with advanced modulation formats, such as quadrature phase-shift keying (QPSK) and quadrature-amplitude modulation (QAM), which enable the corresponding system to...

AI Technical Summary

Benefits of technology

This patent describes an optical receiver with a special component called an optical IQ modulator that generates an optical local-oscillator (OLO) signal for detecting the optical input signal. The receiver also has a phase detector and a phase-lock loop that work together to control the phase of the OLO signal. The phase detector measures the phase difference between the OLO signal and a carrier wave of the input signal. This allows the receiver to be compatible with a specific modulation format called M-QAM. Overall, this technology improves the accuracy and reliability of optical signal detection.

Problems solved by technology

However, a major challenge of this particular transmission format is the need for fast and precise polarization tracking and, in the case of homodyne detection, for phase and carrier-frequency locking of the optical local-oscillator signal.

Images